The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In current Message Transfer Part 3 User Adaptation Layer (M3UA) protocol, Destination User Part Unavailable (DUPU) message is used to notify Application Server Process (ASP) by Signalling Gateway Process (SGP) that the user part of remote peer Message Transfer Part level 3 (MTP3) in No. 7 signaling network node is unavailable. For more information on M3UA protocol, see RFC3332 “Signaling System 7 (SS7) Message Transfer Part 3 (MTP3)-User Adaptation Layer (M3UA)”, which is incorporated herein by reference and further description is omitted.
When determining that the user part of No. 7 signaling destination, namely SPA, is unavailable, the MTP3 of SGP produces MTP-STATUS primitive. M3UA maps the primitive into DUPU message and sends the DUPU message to corresponding ASP as needed. After receiving the DUPU message, ASP acquires the Affected Destination Signaling Point Code (Affected Point Code) from the DUPU message and reports the upper layer user that the destination user part is unavailable.
The DUPU message is sent from SGP to ASP to indicate that the remote destination signaling point user part is unavailable.
The DUPU message carries the following information:
Network AppearanceOptionalRouting ContextOptionalAffected Point CodeMandatoryUser/CauseMandatoryINFO StringOptional
As illustrated in FIG. 1, ASP A and ASP B are provided with Signaling Transfer Point (STP) function and can transfer message from SGP A to SGP B; however ASP A, as an IP STP, may not transmit DUPU messages transparently.
1. When determining that the user part of a No. 7 signaling destination is unavailable, the MTP3 of SGP A produces a MTP-STATUS primitive. M3UA maps the primitive into DUPU message and sends the DUPU message to ASP A as needed. After receiving the message, ASP A acquires the corresponding Affected Point Code from the message and reports the upper layer user that the remote user part is unavailable.
2. Because DUPU message only notifies an adjacent signaling point that the user part of destination signaling point (the destination signaling point is a No. 7 signaling destination signaling point) is unavailable, ASP A only notifies the local upper layer user upon receiving DUPU message; whereas since ASP A immediately notifies local upper layer user that the user part is unavailable as a response to DUPU upon receiving the message, which makes ASP A unable to transmit the message to adjacent signaling point ASP B, so ASP B can not learn that the upper layer user of SP A is not available.